The invention relates to vehicles based on epoxide resins, which after neutralization with bases are dilutable with water and are suitable for aqueous coating materials. It also relates to a method for the synthesis of these vehicles.
The state of the art is the synthesis of water-dilutable, grafted epoxide resins by the reaction of solid epoxide resins with, for instance, carboxylic acid functional monomers, such as (meth)acrylic acid, the acid number of these resins based on the solid resin, ranging from 30 to 320 mg of KOH/g. Such a synthesis is described in the German patent 27 21 822.
Experience has shown that, with such dispersions with an acid number of less than 50, based on the solid resin, a deficient dispersion stability can be observed, which leads to large particles and precipitation phenomena. Aqueous dispersions of grafted epoxide resins with an acid number of less than 30 cannot by synthesized in stable form. For the protection of metallic substrates, it is necessary to obtain films with the lowest possible acid number, in order to achieve the highest protection for the metal.